Process for separating magnesium and like metals which sublime from their ores and compounds



y 1939- H. A. BLACKWELL ET AL 2,165,742

PROCESS FOR SEPARATING MAGNESIUM AND LIKE TADS WHICH SUBLIIE FROM THEIRORES AND COMPOUNDS Filed Sept. 1, 1936 'atented July 11, 1939 PATENTOFFICE PROCESS FOR SEPARATING, MAGNESIUM AND LIKE METALS WHICH SUBLIMEFROM THEIR ORES AND COMPOUNDS Harold Alexandre Blackwell and WilliamLawrence Turner, Garston, England Application September 1, 1936, SerialNo. 98,994 In Great Britain September 4, 1935' 1 Claim. '(CI. 75-40)This invention relates to an improved process for separating magnesium,and like metals which sublime when they are reduced from their ores andcompounds; in the following specification the term "magnesium ore is tobe construed as including ores and compounds of the other metals whichsublime like magnesium.

One of the objects of the present invention is to provide a process forthe production of magnesium metal (a metal which is now in greatercommercial demand than hitherto) which is simple and effective inoperation.

Present processes such as, electrodeposition from solutions or frommolten compounds contuining magnesium or by sublimating froma mixture,contained in a retort, consisting of calcium carbide and a compound ofmagnesium, which is heatedup with fuel or gas, are limited in theircapacity and are methods not favorable for large production.

This invention makes use of the fact that carbonaceous material, siliconand its alloys'and like reducing agents which are electrical conductors,will reduce magnesium from its ores and compounds when the latter are ina direct mixture with the reducing agent if precautions are taken toprevent the vaporized magnesium from combining with any gas, such asoxygen, carbon monoxide, or the like, with which it might come incontact during the reaction and provided that a special heating methodis employed. The reduction of magnesium by smelting with a reducingagent has been carried out in the presence of an inert gas or in a highvacuum to prevent oxidation 01' the reduced metal. The chief dii'll-vculty has been to maintain at the high temperature of reduction which isabove the boiling point of magnesium the necessary conditions for alongenough time to obtain any considerable quantity of magnesium metal. I

The possibility of producing magnesium on a commercial scale is governedby a number of factors. Otthese one of the most important is thesecuring and maintaining of an atmosphere, which, since the reduction ofmagnesium ore is carried out at temperatures above theboiling thereforeis to provide a process and apparatus which makes'the obtaining of theaforesaid desirable-production-factors possible, since smelting ing fromthe smelting process present to attack the distilled metallic vapour,the gases resulting from the smelting process being drawn off at anearly stage by a suction pump.

Another object of the invention is to obtain a high thermal efficiencyin the process by smelting the metal-bearing ore by inter-mixing it witha reducing agent which can be heated by induced currents so thataiiiiiform and rapid heat is produced throughout thecharge.

Another object of the invention is to provide good conditions for theprocess of sublimation in that the smelting process being carried on byinduced currents in the charge it is possible to locate a relativelycold surface close to the charge being smelted, and this acceleratessublimation.

Another object of the invention is to provide a continuous process inwhich the cold surface on which the distilled metallic vapour sublimescan be immediately removed when the charge is spent (for fusion of thecondensate thereon) and a new cold surface or condenser located abovethe mouth of the crucible in which the smelting operation is carried on.

Accordingly the present invention provides a process for separatingmagnesium, and like metals -which sublime, from their ores or compoundswhich comprises mixing and reacting magnesium ore and a reducing agentin physical contact with a mediumffor heating the mix, which is of sucha character that transitory or eddy currents can be generated therein(to heat the medium) by high frequency induction (e. g. from aninduction coil) and under vacuum orpartial vacuum and elevating thetemperature of the-heating medium by the high frequency induction to avalue at which reduction of the magnesium ore and distillation of theresulting metal takes place.

According to a further feature of the present invention there isprovided a processfor separating magnesium and like metals whichsublime, from their ores or compounds which comprises ng and reactingmagnesium ore with such a reducing agent that transitory or eddycurrents can be generated thereimby which currents the reducing agent isheated, by a high frequency induction coil and under vacuum or partialvacuum and elevating the temperature of the mix by high frequencycurrents to a value at which reduction of the magnesium ore anddistillation of theresulting metal take place.

Conveniently in 'carrying\out the process the magnesium vapour, which"is distilled on, is collected in a constantly-evacuated condenser and asufficiently reduced pressure is maintained in the vessel into which themagnesium vapour is distilled to prevent reverse reaction by themagnesium vapour with any of the gases liberated during .the reductionprocess. The reducing agent used in the process may be a carbonaceouscompound, such as graphitic carbon, carbide compound, silicon,aluminium, calcium, or alloys thereof.

One form of apparatus by which the above process is carried out,comprises a crucible, for the ore to be reduced and a reducing agent,located within the field of a high frequency induction coil whereby thecrucible or the contents thereof are heated by induction, and acollector located above the mouth of the crucible and the interior ofwhich is maintained under vacuum or partial vacuum by an exhaust pump.The collector may be in the form of an inverted cone or dome, theexterior surface of which is maintained cool to permit the condensationof the magnesium vapour. Conveniently the collector is detachablymounted in an airtight manner on the mouth of the crucible to permit anew collector to be substituted and the old collector with condensedmagnesium thereon removed for fusion of the condensed magnesium. A highfrequency heating coil may be associated with the collector whereby thecondensed metal can be fused and allowed to flow away therefrom. Aninternal channel may be provided in the interior of the collector at thelower part thereof, this channel being arranged to collect the fusedmagnesium metal condensed on the interior of the collector. Exit fromthis internal channel may be controlled by valve means so that the fusedmetal can be discharged directly into ingot moulds.

One form of apparatus suitable for use in carrying out the process willnow be described with reference to the accompanying diagrammatic drawingwhich is a sectional elevation of a form of high frequency furnace andcondenser collector for the magnesium.

The high frequency furnace is a well known type comprising a steelcontainer i0 provided with an internal copper shield ill and externalstiffening bands l2. The coil is shown at l3 with terminal coilconnections l4. The refractory furn'ace lining i5 is supported byinsulated blocks l6 and I1 and its external surface is cooled by watercirculated through the coil l3 by the inlet and outlet conduits 36 and31.

The collector-condenser I9 is in the form of an inverted dome and has adepending .skirt 24 which extends close to the furnace lining to directthe vapors towards the upper and cooler interior surface of the dome.The exterior of the dome is cooled by water flowing through a coil ofcopper piping 25 which may also serve as a high frequency coil forfusing magnesium which is condensed on the dome. The lower interior partof the dome may have an internal channel 20 (shown in dotted lines) theoutlet of which is controlled by a valve 2| and this channel would serveto collect magnesium fused in situ on the dome and allowed to flow fromthe channel into ingot moulds. The crown of the dome is provided with asuction outlet 22 which is connected to an exhausting air pump 26.

The form of dome shown in full lines may be connected by water cooleddismountable joints 23 to the high frequency furnace. The purpose ofthis arrangement is to permit the dome withthe magnesium condensedthereon to beremoved for fusion of the magnesium and a fresh dome usedfor a new furnace charge. The cooling water may be allowed to flow on tothe joints and collected in the trough 21 and be drained away therefromto a sump. Where the apparatus is worked on continuous lines, that is tosay the collector condenser I9 is removed after each charge and a newcollector'condenser of similar construction substituted for condensing anew charge, then the coil 25 will not be used for fusing the condensedcharge in situ; this fusing operation will be separately performed.

The high frequency alternating current generator used for an inductionfurnace is a wellknown apparatus. The generator which supplies the coilI3 is indicated generally at 28, and as is well-known comprises theusual thermionic valve generator. The mains are indicated at 29 and theleads 30 from the generator are connected to the terminals it forthecoil l3. A similar form'of L generator may be connected to the .coil 25and this generator is indicated at 32, the leads 33 supplying thenecessary energy to the coil 25.

In using the apparatus above described dolomite or magnesite ore ismixed with coke and charged into the space surrounded by the lining B5.The condenser portion is is adjusted and sealed by suitable means suchas bolts 39 and nuts 40 and then with the use of the air pump thereaction chamber formed when the condenser is mounted in position isevacuated of air and gas to a degree sufficient to prevent reversereaction between the magnesium vapor and any gases liberated during thereduction process. The dissociation pressure here defined is meant to bea sufficiently reduced pressure to prevent reverse reaction between themagnesium vapor and any of the gases liberated during the reductionprocess. The high frequency valve is tuned in to give the desiredfrequency of current the periodicity of which is sufliciently high toheat the reducing agent and immediately the carbon reducing agent isincreased in temperature. The heat generated in the carbon reducingagent is localized and in intimate contact with the ore to be reduced,thereby providing ahigh thermal efficiency. The gases initiallyresulting from the application of heat (when the coke is raised to a redheat) may be carbonic acid gas, carbon-monoxide and aqueous vapour.These are quickly eliminated by the suction pump, and the temperature ofthe reducing agent is increased to above the boiling point of magnesiumwhich at normal pressure is of the order of 1100 C. The magnesium metalresulting from the reduction of the ore distils and the vapour risesinto contact with the cold surface of the collector condenser l9 and iscondensed on the inside surface thereof. From there the distillate canbe removed by fusion and cast into ingot moulds. It will be observedthat with the localized heat generated in the charge and thecomparatively cool collector condenser used for the sublimation of themetallic vapour the process of sublimation is accelerated by the largetemperature drop between the furnace and the collector condenser.

The barometric reading must not be allowed to rise above 2 mm. with thereducing agents and ores described, namely, cokeor calcium carbide anddolomite or magnesite) or no magnesium vapour will condense but it willreduce carbon from the carbon-monoxide instead. If the vapour density ofthe mixed vapours is insufficiently reduced (under certaincircumstances) this reverse reaction may occur. -It will be understoodthat there is no objection to maintaining a much higher vacuum and insomecases this is a decided advantage. The magnesium metal will becondensed in large quantities inside the condenser part I9 while carbonmonoxide will be carried away by the pump.

In order to show how such a process can be carried out we now giveexamples of the process:

Example I 12 parts by .weight .of coke and 39 parts by weight ofmagnesite (93% MgO dead burnt) were mixed together, of which 8 parts byweight coke and 39 parts by weight magnesite were crushed and mixedintimately and 4 parts by weight of coke added in the form of lumpsapproximately 1 inches in diameter. These were placed in the containeror crucible, the casing closed and suitably sealed. The whole wasevacuated by the air pump until the pressure indicated was 0.01 mm.barometric reading. The H. F. valve was tuned in and in a few minuteswhen the temperature reached a red heat, magnesium vapour began; todistil off. At 1200 C. magnesium ceased to distiloif and 20 parts byweight of magnesium crystals were recovered in the condenser.

Example II In a further example in which ferro silicon was used as thereducing agent instead of coke,

were crushed and mixed intimately and 12 parts by weight of ferrosilicon were added in the form of lumps approximately inch in diameter.These were" placed in the container or crucible and the casing sealed.The casing was evacuated by an air pump until the pressure indicated wasequal to 0.01 mm. barometric reading. The H. F. valve was tuned in andin a few minutes when the temperature reached a red heat, magnesiumvapour began to distil ofif. At, approximately 1200 C. magnesium ceasedto distil off and 41.8 parts of magnesium crystals Were recovered in thecondenser. A bullet of ferro silicon containing approximately 18%silicon, 82.0% iron remained in the container with the spent charge.

The examples hereinbefore described are given by way of illustration andare not to be construed as a limitation of the invention which isdefined in the following claim.

We claim:

A process for separating magnesium and like metals which sublime frommagnesium and like ores which can be reduced, comprising mixing andreacting magnesium and like ore in subdivided form with graphitic carbonin sub-divided form and heating the reaction mix by high frequencyinduction, the periodicity of which is sufficiently high to heat thereducing agent quickly to the temperature at which reduction of themagnesium ore and distillation of the resulting metal takes placewithout liquefaction or-fusing of the reaction mix, and carrying out thereaction in a continuously evacuated container, pressure of theatmosphere within the container not being permitted to rise above 2 mm.mercury pressure, and condensing the vaporized metal. H. A. BLACKWELL.

W. L. TURNER.

